The heater for use in a glow plug of an automobile engine or the like contains a resistor having a heat-generating portion, a lead, and an insulating base. Materials of the lead and the resistor are selected and shapes of the lead and the resistor are determined so that the resistance of the lead is smaller than the resistance of the resistor (for example, refer to PTL 1).
In recent years, such heaters tend to be used more frequently in a high-temperature environment than before. Therefore, there is a possibility that thermal stress generated in the heater exerts a larger effect than before during a heat cycle.